Method for the manufacture of dental restorations

ABSTRACT

Dental restorations are fabricated using metal powder. Preferably, the metal powder is a high fusing metal and preferably, the metal powder comprises a non-oxidizing metal. The metal powder is applied to a die and is covered with a covering material such as a refractory die material preferably in the form of a flowable paste. A second covering material may be sprinkled or dusted onto the paste. The model is then dried prior to firing. After drying, the model is sintered to provide a high strength metal restoration. After sintering, the outer shell can be broken off easily with one&#39;s hand to expose the sintered coping.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is application is a continuation-in-part application of U.S.patent application Ser. No. 09/912,179, filed Jul. 24, 2001 which is acontinuation-in-part application of U.S. patent application Ser. No.09/757,916, filed Jan. 10, 2001, now U.S. Pat. No. 6,613,273, whichclaims priority to Provisional Application No. 60/175,361 filed Jan. 10,2000, No. 60/182,388 filed Feb. 14, 2000, No. 60/182,155 filed Feb. 14,2000, No. 60/193,591 filed Mar. 30, 2000 and No. 60/201,067 filed May 1,2000, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a method ofmanufacturing dental restorations and restorations produced therefromand more specifically a method of using metal powders to manufacturedental restorations.

BACKGROUND OF THE INVENTION

[0003] Conventional techniques used in the manufacture of dentalrestorations involve the casting of materials such as metals andceramics and employ the “lost wax” process. As known in the industry,the lost wax technique consists of a number of successive operationswhich begin with the dentist taking an impression of the patient'steeth. The impression allows a model or die to be made of the teeth,which the dental technician then uses to build a wax pattern thereon ofthe article to be made. The wax is burned out and the metal, alloy orceramic is cast into the void left by the wax. This process is timeconsuming and involves complex steps.

[0004] Alternative methods have been proposed including those involvingthe sintering of metals. In many of the methods, more than one heatingstep is required to obtain the metal core. In U.S. Pat. No. Re. 33,371,metal powder is applied to a model and heated. A second application ofmetal powder is performed and the model is heated again. In addition tothe many required heating steps, the metallic mixture may run on themodel before sintering, thus damaging the dimensional accuracy of theproduct and making it difficult to achieve consistent thickness.

[0005] In EP 523019, metal powder is applied onto a model and the modelmust then be plunged into a small paper cylinder, filled with amaterial, known as covering material. The material prevents running anddeformation and is mechanically removed when sintering has beenperformed. Although the covering material filled in the cylinder is ableto prevent the material from running, the inventors herein have foundthat the covering material used in the cylinder is too thick, takeslonger to dry, requires high sintering temperatures and promotes tearingand cracking on the metal coping.

[0006] It is desirable that metal restorations be provided having nocracking and tearing problems. It is beneficial that the manufacturingsteps be reduced to provide high strength dental restorations.

SUMMARY OF THE INVENTION

[0007] These and other objects and advantages are accomplished by theprocess wherein metal powder materials are used to form dentalrestorations. In one embodiment herein, metal powder is applied to a dieor model of a tooth for which a restoration will be made. The metalpowder may comprise one or more precious metals, non-precious metals andalloys thereof. Preferably, the metal powder is a high fusing metal andpreferably, the metal powder comprises a non-oxidizing metal. The metalpowder may comprise a multimodal particle size distribution to achievehigh density during sintering. The multimodal particle powder compriseslarger or coarse particle size powder in combination with a smaller orfine particle size powder. After the metal powder is applied to themodel, it is covered with a covering material such as a refractory diematerial preferably in the form of a flowable paste. Optionally, afterthe flowable paste has been applied onto the metal powder, a secondcovering material may be sprinkled or dusted onto the paste. The modelis then dried prior to firing. After drying, the model is sintered toprovide a high strength metal restoration. The sintering range dependsupon the metal or alloy being used. The sintering temperature is closeto but below or in the low range of the melting temperature range of thelayer of alloy powder, or if a metal powder is used, the sinteringtemperature will be close to, but below the melting point of the metalpowder. After sintering, the outer shell can be broken off easily withone's hand to expose the sintered coping. The coping is then easilyremoved from the die absent any adherence problems.

[0008] In an alternate embodiment of the process herein, after a highmelting metal powder has been applied to the die, a mass or ball oflower melting metal or alloy or powder of metal or alloy is placed ordisposed on the metal powder layer. The mass acts as a reservoir ofmaterial which will flow into the metal powder interstices formed fromthe first metal or alloy layer. The process continues as above,whereafter sintering, the outer shell can be broken off easily withone's hand to expose the sintered coping. The coping is then easilyremoved from the die absent any adherence problems.

[0009] In yet another embodiment herein, after the metal powder layer isapplied to the die, a ceramic or porcelain material is applied to theunsintered metal layer. The porcelain appears to act as a thermalbarrier to help in holding the coping in place, prevent margin creepingand lifting. There is no need to apply a covering layer prior tosintering and there is no need to apply an opaque layer after thesintering process and prior to finishing the coping with porcelain toachieve the finally desired product.

[0010] In still another embodiment, a heat-absorbing material is appliedto the die prior to application of the metal layer, and optionally, aheat-absorbing material is further applied onto the metal layer after ithas been formed onto the die, and is also applied onto other components,such as a sprue or reservoir, that may be disposed on the metal layer.The heat-absorbing material increases the absorption of radiant heat toprovide faster, more efficient, sintering kinetics.

[0011] The invention also includes various finishing processes includingpressing ceramic onto the metal coping or applying fiber-reinforcedcomposite materials or polymeric materials to the metal copings.

[0012] The processes and materials herein may be used to manufacturedental appliances including but not limited to orthodontic retainers,bridges, space maintainers, tooth replacement appliances, dentures,posts, crowns, posts, jackets, inlays, onlays, facings, veneers, facets,implants, abutments, splints, partial crowns, teeth, cylinders, pins,and connectors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

[0014]FIG. 1 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein;

[0015]FIG. 2 is the finished restoration of the coping shown in FIG. 1;

[0016]FIG. 3 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein;

[0017]FIG. 4 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein;

[0018]FIG. 5 is an elevational view of a pontic used in accordance witha process herein;

[0019]FIG. 6 is an elevational view of a bar used in accordance with aprocess herein;

[0020]FIG. 7 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein;

[0021]FIG. 8 is an elevational view of the finished restoration of thecoping shown in FIG. 7;

[0022]FIG. 9 shows a coping prior to having a ceramic pellet pressedthereon;

[0023]FIG. 10 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein;

[0024]FIG. 11 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein;

[0025]FIG. 12 is a cross-sectional view of the materials of FIG. 11removed from the die and underfilled with material; and

[0026]FIG. 13 is a cross-sectional view of a die with materials thereonin the manufacture of a dental restoration in accordance with a processherein.

DESCRIPTION OF THE INVENTION

[0027] As will be appreciated, the present invention provides a methodof manufacturing dental restorations using metal powder materials toform the restorations. In one embodiment of the process, a model orduplicate model of a tooth to be restored is fabricated. This involvesknown techniques whereby a dentist takes an impression of the tooth orteeth to be restored. A master die is then prepared from the impressionusing a suitable die material. A duplicate working or refractory die ormodel is made from the original impression or from a duplicateimpression prepared from the master die.

[0028] Metal powder is then applied to the die or model of the tooth forwhich a restoration will be made. Prior to application of metal powder,the die may be coated with a thin layer of die sealer/spacer material orsimilar material such as SinterKor™ Die Spacer available from PentronLaboratory Technologies, LLC, Wallingford, Conn., to seal the die and toprovide easy removal of the restoration from the die at the completionof the sintering operation. Die seal/spacer materials should preferablyleave no residue after burning.

[0029] In one embodiment, optionally, prior to application of the metalpowder, and after the application of the sealer material, or instead ofapplication of the sealer material, a heat-absorbing layer of materialmay be applied to the die. The heat-absorbing layer comprises a materialwhich may or may not withstand the firing temperatures employed in theprocess herein, and that increases the absorption of radiant heat toprovide faster, more efficient, sintering kinetics. Furthermore, moreuniform temperature distribution within the bulk of the material beingheated, is provided. The heat-absorbing material has a low lightreflectance value (LRV). LRV is a measure of the proportion of usefullight reflected by a color. This is generally measured in daylightconditions. The greater the light reflectance value, the lighter thecolor. White and very bright yellows have the highest light reflectancevalues. Bright blues have comparatively low light reflectance values.The light reflectance scale is based on 100, where 0=black and thereforeprovides total light absorption, and white=100 and therefore providestotal light reflection. Due to the variation in shades of white andblack, white reflects about 80 to about 100 percent of the light andblack reflects 0 to about 5 percent of the light.

[0030] For purposes herein, the heat-absorbing layer or coating willhave a low light reflectance value, below about 80, preferably belowabout 50 and most preferably below about 25. The most preferredheat-absorbing coating is black. The heat-absorbing coating may also beconductive and may further be a source for a reducing atmosphere.Depending on the nature of the heat-absorbing coating, it may or may notburn off during sintering operations. Preferably, it burns off duringthe sintering operations. The heat-absorbing coating is preferably adark or colored material. Examples include carbon materials such ascolloidal graphite, carbon black, conductive carbons, graphites, metalflakes, metal powders, and the like. It is preferable that theheat-absorbing material is dispersed in a suitable volatile vehicle suchas alcohol, ketones and the like. The absorbing material may be providedin an amount in the range of about 5 to about 75 percent and preferablyabout 7 to about 50 percent, and most preferably about 8 to about 30percent with respect to the vehicle within which it is dispersed. Onepreferred material is commercially available Grafo 223™ conductivecoating available from Fuchs Lubricants Co., Harvey, Ill. Grafo 223™conductive coating is a graphite-based conductive coating containing 20weight percent solids in an alcohol carrier. The heat-absorbing materialmay be applied to the die directly, or to a sealing layer which has beenapplied to the die, with a brush or by spraying, dipping or similarmeans. Alternatively, the heat-absorbing material may be mixed with arefractory material such as an investment refractory material used tomake the die, and applied to the die or sealant layer. As yet anotheroption, the heat-absorbing material may be mixed in with the materialused to make the die so that it is incorporated into the die and altersthe color of the die, which is typically white, to a dark color.

[0031] The size of the particles of the heat-absorbing material rangefrom about 0.01 microns to about 50 microns. If the heat-absorbingparticles are mixed with a refractive material, the particle size may beas large as 200 microns. The heat-absorbing layer is applied at athickness of about 1 to about 25 microns, and preferably at a thicknessof about 1 to about 10 microns. The heat-absorbing coating improves theprocessing temperatures by decreasing the processing temperatures andprocessing times and enhancing the luster of the finished restoration.Moreover, the heat-absorbing layer will typically burn off partially orcompletely leaving a void. The metal from the metal powder fills in thevoid, providing an aesthically-pleasing, lustrous underlayer. Theheat-absorbing layer may also provide a reducing atmosphere which isdesirable for situations where an oxidizable element or impurities arepart of the sintered restoration.

[0032] The metal powder may be mixed with a binder material to hold themetal particles together for easier application or adaptation to thedie. The combination metal powder/binder is preferably in a paste, tapeor sheet form. Commercially available SinterKor™ materials may be usedherein, available from Pentron Laboratory Technologies, LLC,Wallingford, Conn., and also as disclosed in the SinterKor™ InstructionManual from Jeneric/Pentron, Revision 3.1, 7/2000, which is herebyincorporated by reference for all materials and processes herein.Accordingly, the paste may be pressed onto and around the die or thesheet may be cut to a desired shape to fit onto the die. In mostinstances, it is important that the applied layer extend fully to themargins.

[0033] The thickness of the metal layer is dependent upon therestoration being fabricated. For example, in making abutments, thethickness of the metal layer may range from about 0.1 to about 0.5 mm,and preferably from about 0.1 to about 0.3 mm. In making pontics, thethickness of the metal layer may be greater, and can be accomplishedeither by folding thin layers or forming into a thick mass.

[0034] Typical binder materials include, but are not limited tofiller-free wax, natural wax, mineral3 wax, or an organic waxcomposition may be used which is relatively soft and tacky, ammoniumcaseinate, ammonium stearate, pectin, hexamine, ethyl cellulose,anthracene, triacetyl starch, dulcin, carbazole and tetraphenylethylene. The binder may be mixed with a solvent prior to mixing withthe metal powder. Solvents include, without limitation, propyleneglycol, water, eugenol, light paraffin oil, butyl acetate, butylbenzoate, diacetone alcohol, and dibutyl phthalate. The binder andsolvent are driven off during the sintering process.

[0035] The powder/binder mixture comprises from about 90 to about 99percent powder and from about 1 to about 10 percent binder. Preferably,the powder is present in about 95% by weight and the binder is presentin about 5% by weight.

[0036] The metal powder may comprise one or more precious metals,non-precious metals and alloys thereof. Preferably, the metal powder isa high fusing metal and preferably, the metal powder comprises anon-oxidizing metal. More preferably, the metal powder is selected fromone or more of gold, platinum-Group metals, silver and alloys thereofwhereby the alloys may comprise one or more of the metals in combinationwith one another or with a different metal, such as copper, iridium,rhodium, palladium, indium, tin, gallium and mixtures thereof. Onepreferred alloy comprises about 85 to about 99% Au, 0 to about 15% Pt,and 0 to about 15% of one or more of Ag, Pd, Rh, Ir, In, Ru, and Ta.

[0037] The metal powder may comprise a multimodal particle sizedistribution to achieve high density during sintering. The multimodalparticle powder comprises larger or coarse particle size powder incombination with a smaller or fine particle size powder. The averagesize of the coarse particle powder is about 25 microns, with themajority of the particles exhibiting diameters in the range from about 5to about 100 microns and preferably with the maximum size no greaterthan about 44 microns (−325 mesh) to about 50 microns (−270 mesh). Thefine particle size is less than about 5 microns and preferably less thanabout 2 microns. The coarse particles are present in an amount in therange of about 85 to about 95% by weight and the fine particles arepresent in an amount in the range of about 5 to about 15% by weight ofthe powder.

[0038] After the metal powder has been applied to the die, it may besoaked in a solvent such as alcohol or acetone. After the metal powderis applied to the model, with or without the step of soaking in acetone,it is covered with a covering material such as a refractory diematerial. Typical refractory die materials are compatible with all typesof dental alloys used in dentistry. These materials may be in the formof flowable suspensions or pastes and comprise a powder in combinationwith a liquid vehicle such as alcohol, acetone and the like. It isimportant that the die material is applied at a certain thickness so asto prevent cracking and tearing of the metal restoration duringsintering. It was found that if too thick of a layer is used, crackingand tearing occur on the metal restoration. These materials may be indry powder form (dry technique) or in the form of flowable suspensionsor pastes that comprise a powder in combination with a liquid vehicle(wet technique). When using the wet technique, the refractory layer ispreferably in the range from about 1 to about 8 mm, and more preferably,equal to or below about 5 mm in thickness and most preferably, equal toabout 4 mm in thickness. When the dry technique is used, it isrecommended that a container such as a quartz tube be placed around themodel with the metal thereon to contain the dry powder which surroundsthe model. The thickness of the layer when using the dry technique isapproximately the same as that when using the wet technique. Investmentrefractory materials useful herein include gypsum-bonded,phosphate-bonded or ethyl silicate-bonded investment materials. Theseinvestment materials normally contain up to 80% of a refractory fillersuch as quartz, cristobolite, other forms of silica, leucite or mixturesthereof. These investment materials are commercially available and arewidely used in dental laboratories for various purposes. Examples ofcommercially available investment materials include RapidVest®investment available from Pentron Laboratory Technologies, LLC,Wallingford, Conn.; Accu-Press™ investment available from TalladiumInc., Valencia, Calif.; PC15™ investment available from WhipMixCorporation, Louisville, Ky.; and Speed™ investment available fromIvoclar North America, Amherst, N.Y.

[0039] In addition to the refractory filler, it is preferable that thecovering material contain fibers in an amount of about 0.1 to about 25percent by weight based on the total mixture. It is preferable that thefibers are short in length, preferably, within the range of about 10 nmto about 3 mm and have a diameter in the range from about 5 nm to about100 microns. Preferably, the fibers are non-polymeric to minimizevolatile loss. It is also preferable that the fibers exhibit a highmelting temperature and a low reactivity to prevent reactions at themetal/covering layer interface as well as at the fiber/covering layermatrix interface. Furthermore, it is beneficial that the fibers exhibita low thermal expansion in comparison to the matrix in which the fibersare dispersed. If permeability is desired, longer fibers may be usefulor fibers of polymeric origin may be used.

[0040] The addition of fibers to the covering material createsdiscontinuities and gaps at the fiber/matrix interfaces. The gaps resultfrom the differential expansion between the fibers and the matrix phasesand they help relieve stresses during the heating cycle. Examples offibers useful herein include, but are not limited to, inorganic andorganic fibers. Preferably, as stated above, inorganic fibers are usedto minimize volatile loss. Examples of inorganic fibers include, but arenot limited to, glass, glass-ceramic, ceramic, and metal fibers.Examples of glass fibers include E glass, S glass, and AR glass fibers.Examples of ceramic fibers include alumina, mullite, silica and rockwool fibers. Examples of metal fibers include steel and aluminum metalalloy fibers. Examples of organic fibers include carbon, polyester,polyolefin, polyetheramide, fluoropolymer, polyether, cellulose,phenolic, polyesteramide, polyurethane, epoxy, aminoplastic, silicone,polysulfone, polyetherketone, polyetheretherketone, polyesterimide,polyphenylene sulfide, polyether acryl ketone, poly(amideimide), andpolyimide fibers.

[0041] The addition of fibers to the covering material enables fastdrying and firing during the sintering process without increasingspalling and structural damage, such as cracking and lifting, to thecovering layer. The entire process is more efficient and less techniquesensitive.

[0042] In another embodiment, optionally, after the flowable paste hasbeen applied onto the metal powder, a second covering material may besprinkled or dusted onto the wet paste. The second covering material ispreferably a high temperature refractory powder. It is preferable thatthe high temperature refractory powder is applied directly after thepaste has been applied to prevent slumping and movement of the paste.The high temperature refractory powder improves the green strength ofthe paste material. The externally applied material insulates the metalpowder layer from furnace overshoot during sintering. It is alsobeneficial in breaking and removing the shell from the restoration afterthe sintering process. The removal process is facilitated by the roughtexture created by the high temperature refractory powder. Examples ofthe high temperature refractory powder include but are not limited tohigh temperature refractory oxides such as alumina, silica, and thelike. Preferably, the high temperature refractory powder has a meltingtemperature equal to or greater than about 1200° C.

[0043] The model is then dried prior to firing. After drying, the modelis sintered to provide a high strength metal restoration. The sinteringrange depends upon the metal or alloy being used. The sinteringtemperature is close to but below or in the low range of the meltingtemperature range of the layer of alloy powder, or if a metal powder isused, the sintering temperature will be close to, but below the meltingpoint of the metal powder. After sintering, the outer shell can bebroken off easily with one's hand to expose the sintered coping. Thecoping is then easily removed from the die absent any adherenceproblems.

[0044] In an alternate embodiment, a heat-absorbing layer may be appliedto the metal powder prior to application of the covering layer. Theheat-absorbing layer may be applied directly on the metal powder layeror applied after the metal powder layer has been soaked in a solvent.The same principles apply as those set forth above with respect to theheat-absorbing layer. The materials, properties and procedures discussedabove with respect to the heat-absorbing material are applicable hereand the same is incorporated by reference.

[0045]FIG. 1 illustrates one example of the invention. Die 10 is shownhaving die spacer material 12 applied thereto. Metal powder in the formof a tape 14 is applied to die 10 over die spacer 12. A layer ofrefractory die material 16 is then applied over metal powder layer 10.High temperature refractory powder 18 is shown applied over therefractory die material. The material is then sintered to provide a highstrength dental core material. The outer covering layers are removedfrom what is now core 14 which is further removed from die 10 as shownin FIG. 2. Thereafter, an opaque layer or porcelain or composite isapplied to core 14 to block out the metal followed by a porcelain orcomposite layers 20, such as commercially available Snyspar® porcelainor commercially available Sculpture® composite, both available fromPentron Laboratory Technologies, LLC, Wallingford, Conn., followed byfiring or curing procedures to form the final dental restoration 22.

[0046] In yet another embodiment of the process herein, after a highmelting metal powder has been applied to the die, a mass or ball oflower melting metal or alloy or powder of metal or alloy is placed ordisposed on the metal powder layer. The mass of metal may be bonded,glued, melted or mechanically adhered to the metal powder on the model.The bonding material will have a low melting temperature such that itwill burn out at low temperatures. The mass of metal or alloy may be inthe form of a solid piece of metal, or an ingot or may be an agglomerateor mass of metal or alloy powder held together by a binder. The bindermay be any known binder as discussed above, including but not limitedto, wax, natural wax, mineral wax, or an organic wax composition may beused which is relatively soft and tacky, ammonium caseinate, ammoniumstearate, pectin, hexamine, ethyl cellulose, anthracene, triacetylstarch, dulcin, carbazole, tetraphenyl ethylene and mixtures thereof. Itis preferable that the binder used with the mass of metal or alloypowder be softer than the binder used with the metal powder layer. Thesoft wax in the mass enables the mass to be easily positioned on themetal layer without using force or pressure and thereby preventingdisplacement or distortion of the layer.

[0047] The mass is preferably in the shape or form of a ball, sphere,bar, oval, block, or similar shape. The inventors herein have found thata mass in the shape of an upside down teardrop appears to efficientlydirect and facilitate the flow of the metal of the mass into the metallayer during processing. Regardless of shape, the mass acts as areservoir of material that will flow into the metal powder intersticesformed from the first metal or alloy layer. If a solid metal form isused, it should be coated with a wax or die spacer material in order tocounteract expansion stresses. Preferably, the mass or reservoir isplaced on or proximate the top of the die or model and will flow overand down around the high fusing metal powder on the model during heattreatment and into the interstices of the high fusing metal structure,although placement of the reservoir may be any suitable position toallow the reservoir to flow into the metal or alloy core layer. Powdershaving larger particle sizes compared to the particle size of the metallayer are preferred to make the metal reservoir, such as, as high as 250microns. The mass of the second metal, alloy or powder thereof isapproximately equal to the weight of the first metal or alloy powderlayer.

[0048] The reservoir or mass of metal or alloy may include any lowfusing metal or alloy such as gold, gold alloys, or similar low-fusingalloys. The alloys may contain small amounts of oxidizable elements suchas Ga, Zn, Ge, Ag, Pd, Rh, In, Ru, Cu, Sn, Ta and other precious metals.If an oxidizing element is used in either the metal layer or the mass,provisions can be made to generate a reducing or inert atmosphere toprevent oxidation during the sintering operation. Reducing or inertatmosphere may be created in a variety of ways. Reducing gases such asformic gas or inert gas, e.g., argon, may be disperssed into thesintering chamber. Alternatively, a carbonaceous material may beincorporated onto or placed over the thermal barrier layer describedearlier. One example of placing a carbonaceous material over the barrierlayer is the use of a graphite cover. Otherwise, carbonaceous materialmay be ground into and mixed with the outer covering layer to providereducing atmosphere effects.

[0049] In still another embodiment, prior to the application of thereservoir to the metal powder layer, a sprue is attached to the metalpowder layer. The sprue may be fabricated of the same material as themetal powder layer. One end of the sprue is attached to the metal powderlayer and the other end is attached to the reservoir thereby linking thereservoir to the metal powder layer and reducing the amount of time ofattaching the reservoir to the metal powder layer. One reason for thisis the small cross-section of the sprue. Placement of the spruecorresponds to placement of the reservoir, and hence, the spur is placedon the metal layer at the location that the reservoir will be attached.Thereafter, the reservoir is attached to the other end of the sprue.Preferably, as noted above, the reservoir is placed on or proximate thetop of the die or model. After the restoration has been sintered and isremoved from the covering material, the excess reservoir material shouldbe removed by cutting, grinding, sandblasting or similar means. Theconfiguration of the sprue, which has a much smaller diameter than thereservoir, allows for easy removal of the excess reservoir material.

[0050] Prior to sintering, and after the reservoir has been applied, adie spacer or similar material such as SinterKor™ Die Spacer availablefrom Pentron Laboratory Technologies, LLC, Wallingford, Conn., and/or aheat-absorbing material, as discussed above, may be applied over themetal powder layer and reservoir. After the metal powder and metal masshave been applied to the model or die, the model with the materialsthereon is covered with a covering material, as in the process describedabove, such as a refractory die material such as Polyvest™ materialavailable from Whip-Mix Corp., Kentucky. Prior to covering withrefractory die material, the die may be soaked in a solvent such asalcohol or acetone. Typical refractory die materials are compatible withall types of dental alloys used in dentistry. These materials may be indry powder form (dry technique) or in the form of flowable suspensionsor pastes that comprise a powder in combination with a liquid vehicle(wet technique). Preferably, the liquid vehicle is nonaqueous such asacetone, alcohol and the like. It is important that the die material isapplied at a certain thickness so as to reduce drying time, lowersintering temperature and prevent cracking and tearing of the metalrestoration during sintering. When using the wet technique, therefractory layer is preferably in the range from about 1 to about 8 mm,and more preferably, equal to or below about 5 mm in thickness and mostpreferably, equal to about 4 mm in thickness. When the dry technique isused, it is recommended that a container such as a quartz tube be placedaround the model with the metal thereon to contain the dry powder whichsurrounds the model.

[0051] If the wet technique is used, the model is then dried prior tofiring. After drying, the model is sintered to provide a high strengthmetal restoration. The sintering range depends upon the metal or alloybeing used. The sintering temperature is close to but below or into thelow range of the melting temperature range of the layer of alloy powder,or if a metal powder is used, the sintering temperature will be closeto, but below the melting point of the metal powder. In both cases, thesintering temperature will be higher than the melting temperature rangeor melting point of the metal or alloy reservoir. This heat treatmentallows the reservoir of metal to flow into the interstices of the layerof metal or alloy and form a dense, high strength structure. Aftersintering, the outer shell can be broken off easily with one's hand toexpose the sintered coping. The coping is then easily removed from thedie absent any adherence problems. Alternatively, if the dry techniqueis used, the outer covering layer is easily removed by pushing itthrough the quartz tube.

[0052] Reference is made to FIG. 3 that shows a model 30 with a layer ofmetal powder 32 thereon. Die spacer material 34 is applied prior to theapplication of the layer of metal powder. Thereafter, a spherical-shapedreservoir of metal or alloy 36 is placed proximate the top of the model.Thereafter, a die spacer material 38 is applied on metal layer 32.Refractory covering layer 40 is then applied on and around the precedinglayers and the model is sintered after evaporating acetone or alcoholfrom the surface of the metal. As in the process described above,optionally, after the refractory paste has been applied onto the metalpowder, a high temperature refractory powder is sprinkled or dusted ontothe paste. It is preferable that the high temperature refractory powderis applied directly after the paste has been applied to prevent slumpingand movement of the paste. The high temperature refractory powderimproves the green strength of the paste material. The combination ofboth the paste and the powder insulates the metal powder layer fromfurnace overshoot during sintering. It is beneficial in breaking andremoving the shell from the restoration after the sintering process. Theremoval process is facilitated by the rough texture created by the hightemperature refractory powder. Examples of the high temperaturerefractory powder include but are not limited to high temperaturerefractory oxides such as alumina, silica, and the like. Preferably, thehigh temperature refractory powder has a melting temperature equal to orgreater than about 1200° C. After the covering layers have been removed,the coping is finished with porcelain or composite materials. To assistin bonding the finishing materials to the surface of the coping, abonder coat of metal or alloy material is applied and fired thereto. Thebonder material may contain gold powder with trace amounts of oxidizableelements, such as Cu, In, Sn, Rh, Pd, Ga and mixtures thereof. Pt or Irmay also be included in small quantities.

[0053] In yet another embodiment herein, reference is made to FIG. 4,which shows metal powder layer 40 applied to die 42. A die spacer layer44 may be applied to the die prior to application of layer 40.Thereafter, a ceramic or porcelain material 46 is applied to theunsintered metal layer. The ceramic or porcelain layer may be of athickness necessary to cover the metal core and provide aesthetics.Preferably, the layer is in the range of about 0.1 to about 1.5 mm, andmore preferably in the range of about 0.2 to about 0.5. The model withthe metal and porcelain thereon is thereafter sintered. The porcelain ispreferably an opaque porcelain used in the manufacture of dentalrestorations, such as Synspar® Opaque porcelain available from PentronLaboratory Technologies, LLC, although any porcelain may be used hereinto achieve the final result. The porcelain appears to act as a thermalbarrier to help in holding the coping in place, prevent margin creepingand lifting. There is no need to apply an opaque layer after thesintering process and prior to finishing the coping with porcelain toachieve the finally desired product.

[0054] The process described herein is not limited to single unitrestorations, but is also applicable to multiple unit restorations.FIGS. 5 and 6 illustrate prefabricated pontic 50 and bar 60 for use inthe process of the invention. Bars, pontics, blocks rods and the likemay be in any shape or cross section useful in the manufacture ofmultiple unit restorations such as a square, rectangle, triangle,rhomboid, ovoid, and cylinder. The prefabricated components may besolid, hollow or perforated. The prefabricated component may be a solidcast metal or alloy, an extruded component, or a metal or alloy powdermolded and sintered into a shaped component. Alternatively, thecomponent may be fabricated using metal powder or sheets of metal powderand shaped at the time of fabrication. Such prefabricated, uncuredshapes may be used as needed and desired, such as, for “add on” materialto correct or modify the dental restoration. The shaped forms reduce thetime and labor necessary to create the final dental restorative formedby providing a “starting material” for which to build the desired shape.Similarly, the reservoir material may be provided in a variety of shapesand sizes, such as bars, pontics, rods, cylinders, rectangles and thelike to provide ready to use “reservoirs” which may be cut to thedesired size for application to the dental restoration being formed.Alternately, the component may be a porcelain, ceramic, or fiberreinforced composite material such as Sculpture/FibreKor® material fromPentron Laboratory Technologies, LLC, which component may prefabricatedor made when the restoration is being made. All the aforementionedprocesses described above for single unit restorations are alsoapplicable to multiple unit restorations.

[0055]FIG. 7 shows a die 70 having two abutment teeth sections 72 and74. Sections 72 and 74 show metal powder 76 and 78 thereon. Bar 80 ispositioned therebetween and pontic section 82 is prefabricated as partof bar 80 or, alternatively, is built onto bar 80 similarly to metalpowder layers 76 and 78. Even if bar 80 is provided with a prefabricatedpontic section, metal powder may further be used to build up the ponticsection to the shaped desired. Thereafter, the process continues as setforth above. The entire die is covered with one or more covering layers(refractory die material and a high strength ceramic material) andsintered. The reservoir technique, as described above, may also be usedin this process, whereby reservoirs of metal, alloy or powder of metalsor alloys, are disposed on each section (76, 78, 82) prior to theapplication of the covering layer(s). After sintering, the coveringlayers are removed and the coping is finished with the necessaryporcelain materials. FIG. 8 illustrates the final restoration with theunderlying metal coping 84 and a porcelain finish layer 86.

[0056] An alternative method for finishing any of the restorations(single or multiple unit) made by the processes discussed herein mayinvolve pressing a ceramic material such as OPC® porcelain or Avante®porcelain applying a polymer material or fiber reinforced compositematerial such as Sculpture/FibreKor® or Sculpture® Plus materials, allavailable from Pentron Laboratory Technologies, LLC, onto the metalcoping. After the covering material has been removed from the metalcoping, the metal coping may be opaqued. The latter, along with the diemay be invested using conventional investing techniques. The lost waxprocess is used to create the desired shape for the exterior of thedental restoration. The die with the coping and wax thereon is theninvested in an investment material and the wax is then burned outleaving space for the ceramic to occupy. A ceramic or composite pelletor button is pressed into the investment space to provide the exteriorto the dental restoration. FIG. 9 shows coping 90 disposed on die 92 ininvestment 93. A ceramic button 94 is positioned below plunger 96 and isto be pressed into space 98 created by the lost wax process. This allowsfor cementing into the mouth a ceramic-containing or compositecontaining restoration, which normally must be bonded into the mouth.

[0057] In still yet another embodiment herein, it may be desirable toprovide the coping with a porcelain margin as opposed to a metal margin,for aesthetic purposes. In this instance, when the metal powder isapplied to the die, it does not extend fully to the margins. The metalpowder is applied to a point above the margin or shoulder region on thedie. The process proceeds as above, with the covering layers andsintering step. After sintering, the covering layers are removed. Thecoping is positioned on the die and a porcelain layer such as an opaqueporcelain such as Synspar® Opaque porcelain is applied to the metalcoping, also not extending past the margin. Thereafter, a porcelainmaterial, such as a margin porcelain, is applied onto the lower edge ofthe coping over the porcelain layer and extends to the margin on thedie. The porcelain is preferably a margin porcelain, such as Synspar®Margin Porcelain or Avante® Margin Porcelain, available from PentronLaboratory Technologies, LLC, used in the manufacture of dentalrestorations, although any porcelain with an appropriate coefficient ofthermal expansion which is compatible with the underlying die may beused herein to achieve the final result. By applying porcelain to themargin, the porcelain material is built upon a region lined with nometal and therefore, problems associated with the exposure of the metalat the edge of the coping are overcome. Moreover, the margin of thecoping is strong and not prone to bending or breaking. The porcelainsappear to act as a thermal barrier to help in holding the coping inplace and to prevent margin creeping and lifting. It is then sinteredand the porcelain steps may be repeated again to achieve optimumresults. Thereafter, the coping is built with more porcelain to providethe finally desired exterior of the restoration.

[0058]FIG. 10 depicts a coping of the invention wherein a metal layer100 is applied on die 102 to a point 104 above the margin 106. The metallayer is covered and sintered to obtain coping 100. A porcelain layer108 such as an opaque porcelain is applied on metal coping 100, also topoint 104. A margin porcelain material 110 is applied along margin 106and overlaps the lower edge of metal coping 100 and porcelain layer 108.

[0059] In an alternate embodiment herein, a method of manufacturingdental restorations is provided obviating the need to duplicate themaster die or model of the tooth to be restored. In the process herein,a dentist takes an impression of the tooth or teeth to be restored. Amaster die is then prepared from the impression using a suitable diematerial. From the master die, the actual restoration will be prepared.

[0060] The die as shown in FIG. 11 with all the layers thereon is thendried. Die 111 is shown with metal powder layer 112 applied over diespacer layer 114. Covering layers 116 and 118 are applied thereafter. Asnoted in FIG. 11, the covering layers do not extend past the metallayer, so that all layers can be easily removed as a single unit asshown in FIG. 12. As the layers dry, they dry together to form a singleunit of a metal coping, refractory die and refractory powder.Thereafter, the die having this dried unit of metal coping, refractorydie and refractory powder is soaked in acetone for a period of time,about 8 to 10 minutes. This treatment enables the unit of the metalcoping, refractory die and refractory powder layer to be removed easilyfrom the master die.

[0061] The underside of the coping unit is filled in with a refractorydie material 120 which may be further coated with a refractory powder122 as shown in FIG. 12. These materials are then left to dry,preferably for about ten minutes. The refractory die material is used toprovide a base or platform for the coping unit so that the coping willmaintain its shape during firing. Thereafter, the unit is fired toprovide a high strength metal restoration. The sintering range dependsupon the metal or alloy being used. The sintering temperature is closeto but below the melting temperature of the metal/alloy. Aftersintering, the outer shell can be broken off easily with one's hand toexpose the sintered coping. The coping is then easily removed from thedie absent any adherence problems.

[0062]FIG. 13 depicts a cross-sectional view of a model 130 having diespacer or sealer material 132 thereon. A layer of colloidal graphite 134is then applied onto the layer of sealer material 132, up to the margin.Sinterkor™90⁺ metal powder available from Pentron LaboratoryTechnologies, LLC, Wallingford, Conn., in the form of tape 136 isapplied onto the layer of colloidal graphite. A sprue 138 of the samematerial (Sinterkor™90⁺ metal powder) as the metal powder layer isattached to the metal powder layer, and upon sprue 138 is attachedreservoir 140. Sinterkor™ 24K gold material is used to make reservoir140. The binder in the Sinterkor™ 24K gold material is preferably softerthan the binder used in the Sinterkor™ 90⁺ metal powder layer 136 andsprue 138. This is important so that metal layer 136 and sprue 138 donot become displaced during attachment of reservoir 140. A second layerof colloidal graphite 142 is applied onto metal layer 136, sprue 138,and a portion of reservoir 140. This layer extends beyond the margin. Arefractory covering layer 144 is applied on the layers of materials asshown and the model is sintered. The coping is easily removed from themodel and the resultant coping exhibits a glossy, illustriousundercoating.

[0063] While various descriptions of the present invention are describedabove, it should be understood that the various features can be usedsingly or in any combination thereof. Therefore, this invention is notto be limited to only the specifically preferred embodiments depictedherein.

[0064] Further, it should be understood that variations andmodifications within the spirit and scope of the invention may occur tothose skilled in the art to which the invention pertains.

[0065] Accordingly, all expedient modifications readily attainable byone versed in the art from the disclosure set forth herein that arewithin the scope and spirit of the present invention are to be includedas further embodiments of the present invention. The scope of thepresent invention is accordingly defined as set forth in the appendedclaims.

What is claimed is:
 1. A method for making a dental restorationcomprising: forming a model of one or more teeth; coating the model withmetal or alloy powder; applying a covering material onto the modelcoated with metal or alloy powder wherein the covering material isapplied at a thickness equal to or less than about 8 mm and wherein thecovering material comprises a mixture of refractory powder and fibers;sintering the model coated with metal or alloy powder and coveringmaterial in a furnace to form a coping; and removing the coveringmaterial from the coping.
 2. The method of claim 1 wherein the fibersare selected from the group consisting of inorganic, organic fibers andmixtures thereof.
 3. The method of claim 2 wherein the inorganic fibersare selected from the group consisting of glass, glass-ceramic, ceramic,metal and mixtures thereof.
 4. The method of claim 3 wherein the glassfibers are selected from the group consisting of E glass, S glass, ARglass and mixtures thereof.
 5. The method of claim 3 wherein the ceramicfibers are selected from the group consisting of alumina, mullite,silica, rock wool and mixtures thereof.
 6. The method of claim 3 whereinthe metal fibers are selected from the group consisting of steel,aluminum and mixtures thereof.
 7. The method of claim 2 wherein theorganic fibers are selected from the group consisting of carbon,polyester, polyolefin, polyetheramide, fluoropolymer, polyether,cellulose, phenolic, polyesteramide, polyurethane, epoxy, aminoplastic,silicone, polysulfone, polyetherketone, polyetheretherketone,polyesterimide, polyphenylene sulfide, polyether acryl ketone,poly(amideimide), polyimide fibers and mixtures thereof.
 8. The methodof claim 1 wherein the fibers range from about 0.1 to about 3 mm inlength and from about 1 to about 100 microns in diameter.
 9. The methodof claim 1 wherein the fibers are present in an amount of from about 0.1to about 25 percent by weight and the refractory powder is present in anamount of from about 75 to about 99.9 percent by weight of the totalpowder mixture.
 10. The method of claim 1 wherein the refractory powdercomprises a refractory die material.
 11. The method of claim 1 whereinthe covering material further comprises a liquid vehicle.
 12. The methodof claim 11 wherein the liquid vehicle is selected from alcohol andacetone.
 13. The method of claim 1 further comprising coating thecovering material with a high temperature refractory material.
 14. Themethod of claim 1 wherein the refractory powder comprises silica,leucite or mixtures thereof.
 15. The method of claim 14 wherein thesilica is selected from the group consisting of quartz, cristobolite andmixtures thereof.
 16. The method of claim 11 wherein the refractory diematerial is selected from the group consisting of gypsum-bonded,phosphate-bonded, ethyl silicate-bonded and mixtures thereof.
 17. Themethod of claim 1 further comprising applying a die spacer material tothe model prior to application of the metal or alloy powder.
 18. Themethod of claim 1 wherein applying the covering material onto the modelcoated with metal or alloy powder comprises painting the coveringmaterial onto the metal powder with a brush.
 19. The method of claim 13wherein coating the covering material with a high temperature refractorymaterial comprises dusting the high temperature refractory material ontothe covering material.
 20. A dental restoration formed by the process ofclaim
 1. 21. A method for making a dental restoration comprising:forming a model of one or more teeth; coating the model with metal oralloy powder; covering the model coated with metal powder with acovering material wherein the covering material comprises a mixture ofrefractory powder and fibers; allowing the metal powder and coveringmaterial to dry to form a unit; removing the dried metal powder andcovering material unit from the model; filling the understructure of theunit with covering material wherein the covering material comprises amixture of refractory powder and fibers; sintering the unit in a furnaceto form a coping; and removing the covering material from the coping.22. The method of claim 21 wherein the fibers are selected from thegroup consisting of inorganic, organic fibers and mixtures thereof. 23.The method of claim 22 wherein the inorganic fibers are selected fromthe group consisting of glass, glass-ceramic, ceramic, metal andmixtures thereof.
 24. The method of claim 23 wherein the glass fibersare selected from the group consisting of E glass, S glass, AR glass andmixtures thereof.
 25. The method of claim 23 wherein the ceramic fibersare selected from the group consisting of alumina, mullite, silica, rockwool and mixtures thereof.
 26. The method of claim 23 wherein the metalfibers are selected from the group consisting of steel, aluminum andmixtures thereof.
 27. The method of claim 22 wherein the organic fibersare selected from the group consisting of carbon, polyester, polyolefin,polyetheramide, fluoropolymer, polyether, cellulose, phenolic,polyesteramide, polyurethane, epoxy, aminoplastic, silicone,polysulfone, polyetherketone, polyetheretherketone, polyesterimide,polyphenylene sulfide, polyether acryl ketone, poly(amideimide),polyimide fibers and mixtures thereof.
 28. The method of claim 21wherein the fibers range from about 10 nm to about 3 mm in length andfrom about 5 nm to about 100 microns in diameter.
 29. The method ofclaim 21 wherein the fibers are present in an amount of from about 0.1to about 25 percent by weight and the refractory powder is present in anamount of from about 75 to about 99.9 percent by weight of the totalpowder mixture.
 30. The method of claim 21 wherein the refractory powdercomprises a refractory die material.
 31. The method of claim 21 whereinthe covering material further comprises a liquid vehicle.
 32. The methodof claim 31 wherein the liquid vehicle is selected from alcohol andacetone.
 33. The method of claim 21 further comprising coating thecovering material with a high temperature refractory material.
 34. Themethod of claim 21 wherein the refractory powder comprises silica,leucite or mixtures thereof.
 35. The method of claim 34 wherein thesilica is selected from the group consisting of quartz, cristobolite andmixtures thereof.
 36. The method of claim 30 wherein the refractory diematerial is selected from the group consisting of gypsum-bonded,phosphate-bonded, ethyl silicate-bonded and mixtures thereof.
 37. Themethod of claim 21 further comprising applying a die spacer material tothe model prior to application of the metal or alloy powder.
 38. Themethod of claim 21 wherein applying the covering material onto the modelcoated with metal or alloy powder comprises painting the coveringmaterial onto the metal powder with a brush.
 39. The method of claim 33wherein coating the covering material with a high temperature refractorymaterial comprises dusting the high temperature refractory material ontothe covering material.
 40. A dental restoration formed by the process ofclaim
 21. 41. A method for making a dental restoration comprising:forming a model of one or more teeth; coating the model with powder of afirst metal or alloy; placing a reservoir of a second metal or alloyonto the model coated with the powder of the first metal or alloy,wherein the second metal or alloy has a fusing temperature lower thanthe fusing temperature of the first metal or alloy; covering the modelcoated with the powder of first metal or alloy and the reservoir of thesecond metal or alloy with covering material wherein the coveringmaterial comprises a mixture of refractory powder and fibers; andsintering the model to form a coping.
 42. The method of claim 41 whereinthe fibers are selected from the group consisting of inorganic, organicfibers and mixtures thereof.
 43. The method of claim 42 wherein theinorganic fibers are selected from the group consisting of glass,glass-ceramic, ceramic, metal and mixtures thereof.
 44. The method ofclaim 43 wherein the glass fibers are selected from the group consistingof E glass, S glass, AR glass and mixtures thereof.
 45. The method ofclaim 43 wherein the ceramic fibers are selected from the groupconsisting of alumina, mullite, silica, rock wool and mixtures thereof.46. The method of claim 43 wherein the metal fibers are selected fromthe group consisting of steel, aluminum and mixtures thereof.
 47. Themethod of claim 42 wherein the organic fibers are selected from thegroup consisting of carbon, polyester, polyolefin, polyetheramide,fluoropolymer, polyether, cellulose, phenolic, polyesteramide,polyurethane, epoxy, aminoplastic, silicone, polysulfone,polyetherketone, polyetheretherketone, polyesterimide, polyphenylenesulfide, polyether acryl ketone, poly(amideimide), polyimide fibers andmixtures thereof.
 48. The method of claim 41 wherein the fibers rangefrom about 10 nm to about 3 mm in length and from about 5 nm to about100 microns in diameter.
 49. The method of claim 41 wherein the fibersare present in an amount of from about 0.1 to about 25 percent by weightand the refractory powder is present in an amount of from about 75 toabout 99.9 percent by weight of the total powder mixture.
 50. The methodof claim 41 wherein the refractory powder comprises a refractory diematerial.
 51. The method of claim 41 wherein the covering materialfurther comprises a liquid vehicle.
 52. The method of claim 51 whereinthe liquid vehicle is selected from alcohol and acetone.
 53. The methodof claim 41 further comprising coating the covering material with a hightemperature refractory material.
 54. The method of claim 41 wherein therefractory powder comprises silica, leucite or mixtures thereof.
 55. Themethod of claim 54 wherein the silica is selected from the groupconsisting of quartz, cristobolite and mixtures thereof.
 56. The methodof claim 50 wherein the refractory die material is selected from thegroup consisting of gypsum-bonded, phosphate-bonded, ethylsilicate-bonded and mixtures thereof.
 57. The method of claim 41 furthercomprising applying a die spacer material to the model prior toapplication of the metal or alloy powder.
 58. The method of claim 41wherein applying the covering material onto the model coated with metalor alloy powder comprises painting the covering material onto the metalpowder with a brush.
 59. The method of claim 53 wherein coating thecovering material with a high temperature refractory material comprisesdusting the high temperature refractory material onto the coveringmaterial.
 60. A dental restoration formed by the process of claim 41.61. A method for making a dental restoration comprising: forming a modelof one or more teeth, wherein the model comprises a margin area; coatingthe model with powder of a metal or alloy to a point above the marginarea; covering the model coated with powder with a covering materialwherein the covering material comprises a mixture of refractory powderand fibers; sintering the model coated with powder in a furnace to forma metal coping; removing the covering material from the metal coping;applying a first porcelain material on the metal coping; applying asecond porcelain material on the model along the margin area; and firingthe coping and die coated with first and second porcelain material in afurnace.
 62. The method of claim 61 wherein the fibers are selected fromthe group consisting of inorganic, organic fibers and mixtures thereof.63. The method of claim 62 wherein the inorganic fibers are selectedfrom the group consisting of glass, glass-ceramic, ceramic, metal andmixtures thereof.
 64. The method of claim 63 wherein the glass fibersare selected from the group consisting of E glass, S glass, AR glass andmixtures thereof.
 65. The method of claim 63 wherein the ceramic fibersare selected from the group consisting of alumina, mullite, silica, rockwool and mixtures thereof.
 66. The method of claim 63 wherein the metalfibers are selected from the group consisting of steel, aluminum andmixtures thereof.
 67. The method of claim 62 wherein the organic fibersare selected from the group consisting of carbon, polyester, polyolefin,polyetheramide, fluoropolymer, polyether, cellulose, phenolic,polyesteramide, polyurethane, epoxy, aminoplastic, silicone,polysulfone, polyetherketone, polyetheretherketone, polyesterimide,polyphenylene sulfide, polyether acryl ketone, poly(amideimide),polyimide fibers and mixtures thereof.
 68. The method of claim 61wherein the fibers range from about 10 nm to about 3 mm in length andfrom about 5 nm to about 100 microns in diameter.
 69. The method ofclaim 61 wherein the fibers are present in an amount of from about 0.1to about 25 percent by weight and the refractory powder is present in anamount of from about 75 to about 99.9 percent by weight of the totalpowder mixture.
 70. The method of claim 61 wherein the refractory powdercomprises a refractory die material.
 71. The method of claim 61 whereinthe covering material further comprises a liquid vehicle.
 72. The methodof claim 71 wherein the liquid vehicle is selected from alcohol andacetone.
 73. The method of claim 61 further comprising coating thecovering material with a high temperature refractory material.
 74. Themethod of claim 61 wherein the refractory powder comprises silica,leucite or mixtures thereof.
 75. The method of claim 74 wherein thesilica is selected from the group consisting of quartz, cristobolite andmixtures thereof.
 76. The method of claim 70 wherein the refractory diematerial is selected from the group consisting of gypsum-bonded,phosphate-bonded, ethyl silicate-bonded and mixtures thereof.
 77. Themethod of claim 61 further comprising applying a die spacer material tothe model prior to application of the metal or alloy powder.
 78. Themethod of claim 61 wherein applying the covering material onto the modelcoated with metal or alloy powder comprises painting the coveringmaterial onto the metal powder with a brush.
 79. The method of claim 73wherein coating the covering material with a high temperature refractorymaterial comprises dusting the high temperature refractory material ontothe covering material.
 80. A dental restoration formed by the process ofclaim
 61. 81. A method for making a dental restoration comprising:forming a model of one or more teeth; placing a bar or pontic on themodel; coating the model and bar or pontic with metal or alloy powder;applying a covering material onto the model coated with metal or alloypowder wherein the covering material comprises a mixture of refractorypowder and fibers; sintering the model coated with metal or alloy powderand covering material in a furnace to form a coping; and removing thecovering material from the coping.
 82. The method of claim 81 whereinthe fibers are selected from the group consisting of inorganic, organicfibers and mixtures thereof.
 83. The method of claim 82 wherein theinorganic fibers are selected from the group consisting of glass,glass-ceramic, ceramic, metal and mixtures thereof.
 84. The method ofclaim 83 wherein the glass fibers are selected from the group consistingof E glass, S glass, AR glass and mixtures thereof.
 85. The method ofclaim 83 wherein the ceramic fibers are selected from the groupconsisting of alumina, mullite, silica, rock wool and mixtures thereof.86. The method of claim 83 wherein the metal fibers are selected fromthe group consisting of steel, aluminum and mixtures thereof.
 87. Themethod of claim 82 wherein the organic fibers are selected from thegroup consisting of carbon, polyester, polyolefin, polyetheramide,fluoropolymer, polyether, cellulose, phenolic, polyesteramide,polyurethane, epoxy, aminoplastic, silicone, polysulfone,polyetherketone, polyetheretherketone, polyesterimide, polyphenylenesulfide, polyether acryl ketone, poly(amideimide), polyimide fibers andmixtures thereof.
 88. The method of claim 81 wherein the fibers rangefrom about 10 nm to about 3 mm in length and from about 5 nm to about100 microns in diameter.
 89. The method of claim 81 wherein the fibersare present in an amount of from about 0.1 to about 25 percent by weightand the refractory powder is present in an amount of from about 75 toabout 99.9 percent by weight of the total powder mixture.
 90. The methodof claim 81 wherein the refractory powder comprises a refractory diematerial.
 91. The method of claim 81 wherein the covering materialfurther comprises a liquid vehicle.
 92. The method of claim 91 whereinthe liquid vehicle is selected from alcohol and acetone.
 93. The methodof claim 81 further comprising coating the covering material with a hightemperature refractory material.
 94. The method of claim 81 wherein therefractory powder comprises silica, leucite or mixtures thereof.
 95. Themethod of claim 94 wherein the silica is selected from the groupconsisting of quartz, cristobolite and mixtures thereof.
 96. The methodof claim 90 wherein the refractory die material is selected from thegroup consisting of gypsum-bonded, phosphate-bonded, ethylsilicate-bonded and mixtures thereof.
 97. The method of claim 81 furthercomprising applying a die spacer material to the model prior toapplication of the metal or alloy powder.
 98. The method of claim 81wherein applying the covering material onto the model coated with metalor alloy powder comprises painting the covering material onto the metalpowder with a brush.
 99. The method of claim 81 wherein coating thecovering material with a high temperature refractory material comprisesdusting the high temperature refractory material onto the coveringmaterial.
 100. A dental restoration formed by the process of claim 81.101. A method for making a dental restoration comprising: forming amodel of one or more teeth; coating the model with powder of a firstmetal or alloy; attaching a sprue to the model coated with the powder ofthe first metal or alloy; attaching a reservoir of a second metal oralloy onto the sprue, wherein the second metal or alloy has a fusingtemperature lower than the fusing temperature of the first metal oralloy; covering the model coated with the powder of the first metal oralloy and the mass of the second metal or alloy with covering material,wherein the covering material comprises a mixture of refractory powderand fibers; and sintering the model.
 102. The method of claim 101wherein the fibers are selected from the group consisting of inorganic,organic fibers and mixtures thereof.
 103. The method of claim 102wherein the inorganic fibers are selected from the group consisting ofglass, glass-ceramic, ceramic, metal and mixtures thereof.
 104. Themethod of claim 103 wherein the glass fibers are selected from the groupconsisting of E glass, S glass, AR glass and mixtures thereof.
 105. Themethod of claim 103 wherein the ceramic fibers are selected from thegroup consisting of alumina, mullite, silica, rock wool and mixturesthereof.
 106. The method of claim 103 wherein the metal fibers areselected from the group consisting of steel, aluminum and mixturesthereof.
 107. The method of claim 102 wherein the organic fibers areselected from the group consisting of carbon, polyester, polyolefin,polyetheramide, fluoropolymer, polyether, cellulose, phenolic,polyesteramide, polyurethane, epoxy, aminoplastic, silicone,polysulfone, polyetherketone, polyetheretherketone, polyesterimide,polyphenylene sulfide, polyether acryl ketone, poly(amideimide),polyimide fibers and mixtures thereof.
 108. The method of claim 101wherein the fibers range from about 10 nm to about 3 mm in length andfrom about 5 nm to about 100 microns in diameter.
 109. The method ofclaim 101 wherein the fibers are present in an amount of from about 0.1to about 25 percent by weight and the refractory powder is present in anamount of from about 75 to about 99.9 percent by weight of the totalpowder mixture.
 110. The method of claim 101 wherein the refractorypowder comprises a refractory die material.
 111. The method of claim 101wherein the covering material further comprises a liquid vehicle. 112.The method of claim 111 wherein the liquid vehicle is selected fromalcohol and acetone.
 113. The method of claim 101 further comprisingcoating the covering material with a high temperature refractorymaterial.
 114. The method of claim 101 wherein the refractory powdercomprises silica, leucite or mixtures thereof.
 115. The method of claim114 wherein the silica is selected from the group consisting of quartz,cristobolite and mixtures thereof.
 116. The method of claim 1 10 whereinthe refractory die material is selected from the group consisting ofgypsum-bonded, phosphate-bonded, ethyl silicate-bonded and mixturesthereof.
 117. The method of claim 101 further comprising applying a diespacer material to the model prior to application of the metal or alloypowder.
 118. The method of claim 101 wherein applying the coveringmaterial onto the model coated with metal or alloy powder comprisespainting the covering material onto the metal powder with a brush. 119.The method of claim 113 wherein coating the covering material with ahigh temperature refractory material comprises dusting the hightemperature refractory material onto the covering material.
 120. Adental restoration formed by the process of claim
 101. 121. A method formaking a dental restoration comprising: forming a model of one or moreteeth; applying a first layer of a heat-absorbing material to the model;applying a powder of a first metal or alloy onto the heat-absorbingmaterial; covering the model coated with the powder of the first metalor alloy with covering material, wherein the covering material comprisesa mixture of refractory powder and fibers; and sintering the model. 122.The method of claim 121 wherein the fibers are selected from the groupconsisting of inorganic, organic fibers and mixtures thereof.
 123. Themethod of claim 122 wherein the inorganic fibers are selected from thegroup consisting of glass, glass-ceramic, ceramic, metal and mixturesthereof.
 124. The method of claim 123 wherein the glass fibers areselected from the group consisting of E glass, S glass, AR glass andmixtures thereof.
 125. The method of claim 123 wherein the ceramicfibers are selected from the group consisting of alumina, mullite,silica, rock wool and mixtures thereof.
 126. The method of claim 123wherein the metal fibers are selected from the group consisting ofsteel, aluminum and mixtures thereof.
 127. The method of claim 122wherein the organic fibers are selected from the group consisting ofcarbon, polyester, polyolefin, polyetheramide, fluoropolymer, polyether,cellulose, phenolic, polyesteramide, polyurethane, epoxy, aminoplastic,silicone, polysulfone, polyetherketone, polyetheretherketone,polyesterimide, polyphenylene sulfide, polyether acryl ketone,poly(amideimide), polyimide fibers and mixtures thereof.
 128. The methodof claim 121 wherein the fibers range from about 10 nm to about 3 mm inlength and from about 5 nm to about 100 microns in diameter.
 129. Themethod of claim 121 wherein the fibers are present in an amount of fromabout 0.1 to about 25 percent by weight and the refractory powder ispresent in an amount of from about 75 to about 99.1 percent by weight ofthe total powder mixture.
 130. The method of claim 121 wherein therefractory powder comprises a refractory die material.
 131. The methodof claim 121 wherein the covering material further comprises a liquidvehicle.
 132. The method of claim 131 wherein the liquid vehicle isselected from alcohol and acetone.
 133. The method of claim 121 furthercomprising coating the covering material with a high temperaturerefractory material.
 134. The method of claim 121 wherein the refractorypowder comprises silica, leucite or mixtures thereof.
 135. The method ofclaim 134 wherein the silica is selected from the group consisting ofquartz, cristobolite and mixtures thereof.
 136. The method of claim 130wherein the refractory die material is selected from the groupconsisting of gypsum-bonded, phosphate-bonded, ethyl silicate-bonded andmixtures thereof.
 137. The method of claim 121 further comprisingapplying a die spacer material to the model prior to application of themetal or alloy powder.
 138. The method of claim 121 wherein applying thecovering material onto the model coated with metal or alloy powdercomprises painting the covering material onto the metal powder with abrush.
 139. The method of claim 134 wherein coating the coveringmaterial with a high temperature refractory material comprises dustingthe high temperature refractory material onto the covering material.140. A dental restoration formed by the process of claim 121.